Motor vehicle suspension systems are configured so that the wheels are able to follow elevational changes in the road surface as the vehicle travels therealong. When a rise in the road surface is encountered, the suspension responds in “jounce” in which the wheel is able to move upwardly relative to the frame of the vehicle. On the other hand, when a dip in the road surface is encountered, the suspension responds in “rebound” in which the wheel is able to move downwardly relative to the frame of the vehicle. In either jounce or rebound, a spring (ie., coil, leaf, torsion, etc.) is incorporated at the wheel in order to provide a resilient response to the respective vertical movements with regard to the vehicle frame. However, in order to prevent wheel bouncing and excessive vehicle body motion, a shock absorber is placed at the wheel to dampen wheel bounce. Additionally, when the limit of jounce is encountered, it is customary to provide a maximum jounce impact absorber in the form of a bump cushion.
Referring now to FIGS. 1 through 1B, components of a conventional suspension system 10 are depicted which allow for jounce and rebound at a wheel of the subject motor vehicle 12.
Firstly with regard to FIG. 1, a control arm 14 is pivotally mounted with respect to the frame 16, wherein, in the depicted example, a torsion spring 18 is utilized to provide resilient response for the jounce and rebound of the control arm relative to the frame. To provide control over bounce, a shock absorber 20 is connected pivotally at one end to the frame 16 and connected pivotally at the other end to the control arm 14. To provide cushioning in the event a maximum jounce occurs, a bump cushion 22 is mounted to the frame 16 which is resiliently compressed by movement of the control arm as jounce approaches its maximum.
Referring next to FIG. 1A, the internal components and operational aspects of a conventional shock absorber 20′ (a remote reservoir high pressure gas type shock absorber being shown merely by way of example) can be understood. A valved piston 30 is reciprocably movable within a shock cylinder 32. A shock rod 34 is attached to the valved piston 30 and is guided by a shock rod guide 36 at one end of the shock cylinder 32. Below the valved piston 30 and above the shock rod guide 36 is a mutually interacting rebound limiter 38. The instantaneous position of the valved piston 30 within the shock cylinder 32 defines a first interior portion 32F and a second interior portion 32S of the interior of the shock cylinder. In the example depicted at FIG. 1A, the pressurization in the first and second interior portions 32F, 32S is provided by an oil O which is pressurized by pressurized gas, preferably nitrogen, G acting on a divider piston 40 of an oil reservoir cylinder 42, wherein a tube 44, including a base valve 44V, connects the oil between the oil reservoir cylinder and the first interior portion. In operation, as the control arm undergoes jounce, the oil is displaced from the first interior portion into the oil reservoir cylinder, causing the pressure of the nitrogen gas to increase as its volume decreases and thereby causing an increased hydraulic pressure on the valved piston 30 in a direction toward the shock rod guide. Oil is able to directionally meter through valving 46 of the valved piston 30 in a manner which provides damping.
Referring next to FIG. 1B, the internal structure of a conventional bump cushion 22 can be understood. An optional skin 50 of a pliant plastic material may (or may not) overlay an interior of resilient elastomeric material 52, which may be for example a rubber, rubber-like material, or micro-cellular urethane. In operation as the control arm approaches maximum jounce, the bump cushion 22 compresses, delivering a reaction force on the control arm which increases with increasing compression so as to minimize the severity of impact of the control arm with respect to the frame at the limit of jounce. Immediately following the jounce, the rebound involves the energy absorbed by the compression of the conventional bump cushion being delivered resiliently back to the suspension.
In the art of motor vehicle off-road racing, it is known (for at least the past 15 years) to replace a conventional bump cushion with a device which better accommodates extremes of control arm jounce, known as an “air-bump stop” or “bumpshock”.
As depicted by way of exemplification at FIG. 2, a conventional air-bump stop 60 has an elongated cylinder 62 and a valved piston 64 which is reciprocably movable within the cylinder. The valved piston 64 demarcates a primary chamber 66 and a secondary chamber 68, which mutually communicate through the valving 70 of the valved piston. A rod 72 is attached to the valved piston 64 and is guided by a rod seal 74 at the terminous of the secondary chamber 68 and a rod guide 76 at one end of the cylinder 62. Both the primary and secondary chambers 66, 68 are pressurized by a pressurized gas G, most preferably nitrogen, which is mixed with oil O. In operation of the example depicted at FIG. 2, as a control arm undergoes jounce, the piston 64 moves into the primary chamber 66. As this occurs, oil O is metered through the valving 70 at a predetermined flow rate based upon the pressure of the piston applied by the control arm jounce, with the consequence that the gas in the primary chamber 66 increases in pressure rapidly which pressure on the piston reacts against the jounce. Additionally, an “air spring” function due to the total pressure within the primary and secondary chambers acts on the area of the rod 72 to provide an exponential force as related to rod movement into the cylinder.
What remains needed in the art is an improved motor vehicle suspension system in which better accommodation of jounce and rebound is provided than by a conventional shock absorber, conventional bump cushion and/or conventional air-bump stop.